Exhaust gas emitted from an internal combustion engine such as a gasoline engine, diesel engine, etc., for an automobile and the like, contains components such as carbon monoxide (CO), hydrocarbon (HC), and nitrogen oxide (NOx).
Therefore, an exhaust gas purifying apparatus for decomposing and removing these components is generally provided in the internal combustion engine, and the components are substantially decomposed by an exhaust gas purification catalyst installed in the exhaust gas purifying apparatus. As such an exhaust gas purification catalyst, for example, a three-way catalyst, or a NOx storage/reduction catalyst has been known.
The three-way catalyst is a catalyst of simultaneously performing oxidation of CO and HC and reduction of NOx in a stoichiometric (theoretical air-fuel ratio) atmosphere.
The NOx storage/reduction catalyst is a catalyst where NOx in the exhaust gas is stored in a lean atmosphere and the NOx is reduced to nitrogen (N2) in stoichiometric and rich atmospheres, and this catalyst cleverly utilizes the change of exhaust gas components in lean, stoichiometric, and rich atmospheres.
However, even when such a catalyst is employed, there is a problem in the purification of exhaust gas, and various studies have been made thereon.
In the catalyst for exhaust gas purification of Japanese Unexamined Patent Publication No. 2006-043637, a NOx storing material selected from the group consisting of an alkali metal, an alkaline earth metal, and a rare earth element; and a catalytic noble metal is supported on composite oxide support particles containing Al, Zr, and Ti. Then, the composite oxide support particles are porous, and the volume of pores having a diameter of 20 nm or less is 0.4 ml/g or more.
The catalyst support particles for exhaust gas purification of Japanese Unexamined Patent Publication No. 2013-252465 contain a phosphate, etc., represented by the formula: MPO4 (wherein M is Y, La, or Al).